Master cylinder for a regulated braking system

ABSTRACT

A master cylinder for a regulated braking system having at least one piston, which is movable in a housing and which is sealed from a pressure chamber by a sealing element arranged in a ring groove of the housing, which can be connected to an unpressurized supply chamber by control passages designed in the pistons. In order to reduce the flow resistance of the control passages at the same dead stroke, the control passages have a control edge designed parallel to a piston end face of at least one of the pistons.

The invention relates to a master cylinder for a regulated brakingsystem having at least one piston, which is movable in a housing andwhich is sealed off by means of a sealing element arranged in an annulargroove of the housing from a pressure chamber, which can be connected toan unpressurized replenishment chamber by means of control passagesformed in the piston.

A master cylinder of this kind is known from DE 10 2004 057 137 A1, forexample, wherein the control passages are provided as radial transverseholes of small cross section and an encircling inner groove is formed onan inner side in the region of the transverse holes in order to minimizethe idle travel of the master cylinder and, at the same time, to reducethe throttling resistance by reducing the length of the transverseholes.

In the case of use in a regulated braking system, such as a brakingsystem with anti-slip regulation (ASR) or an electronic stabilityprogram (ESP), additional pressure medium is drawn in from a pressuremedium reservoir via the master cylinder by a pump in the case of acontrol intervention. The disadvantage here is that the small crosssection of the transverse holes produces an excessive flow resistance,and the pressure medium required cannot be made available quickly enoughto the pump.

In order to reduce the flow resistance, there is the possibility, in thecase of the known master cylinders, of providing a larger number oftransverse holes or of optimizing the transverse holes in respect of thediameter thereof. However, a disadvantage of the first-mentionedsolution is found to be the fact that the flow resistance is reduced infavor of the stability of the piston and, furthermore, that theprovision of a large number of small transverse holes is economicallydisadvantageous. The second solution has the disadvantage that the idletravel (closing travel) of the master cylinder is increased bydisplacing the controlling lateral edge of the holes.

It is therefore the underlying object of the invention to provide amaster cylinder which is improved in respect of the stated disadvantagesof the known master cylinder.

According to the invention, the object is achieved by virtue of the factthat the control passages of at least one of the pistons have a controledge formed parallel to a piston end face. This makes it possible toincrease the flow cross section of the control passages while keepingthe closing travel the same, thereby making it possible to improvedynamic behavior during control interventions.

The control passages are preferably provided as axial grooves on anouter side of the piston. The axial grooves offer the advantage thatdefined guidance of the sealing element on the outer side of the pistonis ensured.

A large contact area of the piston with the sealing element or the innersealing lip thereof and, at the same time, a large groove cross sectioncan be achieved if the axial grooves are provided in a dovetail shape.

In contrast, an alternative embodiment of the invention makes provisionfor the control passages to be provided as radial apertures in thepiston. Here too, guidance for the sealing element on the piston isprovided.

Parallelism can be produced in a simple manner if the control passagesare provided in the piston by stamping.

According to an advantageous embodiment of the invention, the piston ismade of plastic, making the piston simple and economical to produce.

Another advantageous embodiment envisages that the piston is produced bymeans of an extrusion process.

The piston is preferably of cup-shaped design with a bottom, and afirst, centrally arranged fixing element for a return spring of thepiston is provided on an inner side of the bottom.

If the master cylinder has a sensor arrangement for monitoring theposition and movement of a piston, then, according to an advantageousembodiment, a second, centrally arranged fixing element for a magneticguide element is provided on an outer side of the bottom.

Further features, advantages and possible applications of the inventionwill emerge from the dependent claims and the following description ofillustrative embodiments and with reference to the drawing.

In the drawing, in which each of the figures is highly schematized:

FIG. 1 shows a master cylinder according to the invention in a firstillustrative embodiment, having a first and a second piston, inlongitudinal section;

FIG. 2 shows a partial view of the second piston in accordance with FIG.1 in three-dimensional representation;

FIG. 3 shows another partial view of the second piston in accordancewith FIG. 1 in three-dimensional representation and in partial section;

FIG. 4 shows another partial view of the second piston in accordancewith FIG. 1 in three-dimensional representation;

FIG. 5 shows a master cylinder according to the invention in a secondillustrative embodiment, having a first and a second piston, inlongitudinal section;

FIG. 6 shows a piston in a third illustrative embodiment inthree-dimensional representation, and

FIG. 7 shows an enlarged detail of the piston shown in FIG. 6.

FIG. 1 shows a longitudinal section through a master cylinder 1according to the invention in a first illustrative embodiment, which isused in a regulated braking system with anti-slip regulation (ASR)and/or an electronic stability program (ESP), for example, and is ofplunger- and tandem-type design.

The master cylinder 1 comprises a first and a second piston 3, 4, whichis movable in a housing 2, wherein a sealing element 7, 8 in the form ofa circular ring and having an inner sealing lip 9, 10 subject to dynamicforces and an outer sealing lip 11, 12 subject to static forces isprovided in an annular groove 5, 6 of the housing 2. The inner sealinglip 9, 10 subject to dynamic forces rests by means of a first sealingsurface on the piston 3, 4, and the outer sealing lip 11, 12 subject tostatic forces rests by means of a second sealing surface on a bottom ofthe annular groove 5, 6. An outer side 13, 14 of the pistons 3, 4 servesas a guide surface.

In an unactuated state of the master cylinder 1, which is illustrated inFIG. 1, a first and a second pressure chamber 15, 16 are connected to anunpressurized pressure medium reservoir (not shown) via a pressuremedium channel (not shown) and a replenishment chamber 17, 18 in thehousing 2 and via control passages 19, 20 in a cup-shaped wall 21, 22 ofthe first and the second piston 3, 4. In this arrangement, the pistons3, 4 are preloaded by means of return springs 23, 24.

The return spring 23, 24 is in each case arranged at least partiallywithin the cup-shaped wall 21, 22. As can be seen from FIG. 1, a centricpeg 25 projects centrally within the wall 21 of the first piston 3, saidpeg ending before it emerges axially from the wall 21. This end 26 isprovided with a stop 27 for a sleeve 28, which interacts with a collar29 in such a way that the sleeve 28 can be telescoped to a limitedextent relative to the peg 25. In other words, the sleeve 28 is urgedinto the interior of the piston by the return spring 23 upon actuation.As is apparent, the stop 27 is preferably an annular disk, which isriveted—in particular wobble-riveted—to the peg 25. The other end of thesleeve 28 has the dish-type collar 29 for contact with the return spring23.

At the bottom 31 of the second piston 4, said piston has a first fixingelement 32, which extends centrally within the wall 22 from an innerside of the bottom 31 in order to fix and position the return spring 24.

To actuate the master cylinder 1, the first piston 3 is moved inactuating direction A. During this process, the movement of the firstpiston 3 is transmitted to the second piston 4 by the return spring 23.As soon as the control edges 33, 34 (described in greater detail below)of the control passages 19, 20 are in the region of the sealing elements7, 8, i.e. the control edges 33, 34 have been crossed, the “idle travel”(closing travel) of the master cylinder 1 has been traversed since nomore pressure medium can pass from the replenishment chambers 17, 18into the pressure chambers 15, 16 via the control passages 19, 20. Theconnection between the pressure chambers 15, 16 and the pressure mediumreservoir is interrupted, and pressure is built up in the pressurechambers 15, 16.

In the case of an ASR or ESP intervention, it may be necessary to drawadditional pressure medium in the direction of the wheel brakes from thepressure medium reservoir via the pressure chamber or chambers 15, 16,whether the pistons 3, 4 are actuated or unactuated, this preferablybeing accomplished by means of a pump, the inlet of which can beconnected either to the pressure chambers 15, 16 of the master cylinder1 or to the wheel brakes in order to deliver in the direction of thewheel brakes or in the direction of the master cylinder 1 (recirculationprinciple). For this purpose, the additional pressure medium is drawnfrom the pressure medium reservoir via the pressure medium channels, thereplenishment chambers 17, 18, the control passages 19, 20 and thepressure chambers 15, 16 in the case of an ASR or ESP intervention inthe unactuated state of the master cylinder 1. In the case of an ESPintervention in the actuated state of the master cylinder 1, additionalpressure medium is also drawn in by flow across the outer sealing lips11, 12 of the sealing elements 7, 8 since they are folded over in thedirection of the inner sealing lips 9, 10 by the intake pressure and, asa result, the sealing surface of the outer sealing lip 11, 12 no longerrests on the bottom of the annular groove 5, 6. In order to makeavailable sufficient pressure medium quickly to the pump in the case ofan ASR or ESP intervention, especially in the unactuated state of themaster cylinder 1, it is necessary to minimize the flow resistance ofthe control passages 19, 20, although the idle travel of the mastercylinder 1 should also be kept as small as possible.

In the region of the control passages 19 of the first piston 3, a radialencircling inner groove 35 is provided on an inner side of the piston 3in order to reduce the throttling resistance, said groove shortening thelength of the control passages 19, which are provided as radialtransverse holes.

FIGS. 2 to 4 show partial views of the second piston 4 in an enlarged,partially sectioned three-dimensional representation.

In order to enlarge the area of flow of the control passages 20 of thesecond piston 4, the control passages 20 have a control edge 34 which isformed parallel to a piston end face 36.

This makes it possible to enlarge the flow cross section of the controlpassages 20 while keeping the closing travel the same, thus enabling thedynamic behavior of the master cylinder 1 to be improved during controlinterventions.

As is apparent, the control passages 20 according to the illustrativeembodiment shown are designed as axial grooves on the outer side 14 ofthe piston 4. These can be introduced into the piston 4 in a simplemanner, e.g. by forming or stamping, if the piston 4 is made of plastic,making the piston 4 simple and economical to produce. The stability ofthe piston 4 is not affected by the axial grooves since the piston 4 canhave a relatively thick wall 22, without disadvantages in respect ofweight and other necessary properties.

An alternative embodiment envisages that the piston 4 be produced bymeans of an extrusion process. Aluminum can be provided as a material inthis case, for example. Here too, the parallel control edges 34 and alsothe axial grooves can be provided in a simple manner.

As shown in FIG. 3, one groove end 54 of the axial grooves can be oftapered design, and an embodiment with a radius (convex or concave) islikewise conceivable within the scope of the invention. Different grooveshapes are also possible. These can be introduced into the piston 4 in asubstantially dovetail shape, for example, as shown. The dovetail grooveshape has the advantage that the contact surface of the piston 4 withthe sealing element 8 or the inner sealing lip 10 thereof is enlargedand, at the same time, a large flow cross section can be formed throughan enlarged diameter of the groove at the groove base.

However, rectangular, undulating, round or V-shaped grooves are alsopossible.

The control passages 20 described furthermore have the advantage that acollar heel 37 of the sealing element 8 is guided in a defined manner onthe outer side 14 of the piston 14 and cannot enter the control passages20. Such a risk would exist in the case of an encircling groove, forexample.

As can be seen from FIG. 3, the first fixing element 32 is provided inthe form of three arms, wherein the individual arms 38 are of beveleddesign to simplify the installation and positioning of the return spring24.

FIG. 4 shows an external view of the bottom 31 of the second piston 4.It is apparent that a second, centrally arranged fixing element 39 inthe form of a circular projection extends from an outer side of thebottom 31. This performs its function when, in accordance with thesecond embodiment described below and shown in FIG. 5, the mastercylinder 1 has a sensor arrangement for monitoring the position andmovement of the piston 3, and a magnetic guide element 40 rests on thesecond piston 4.

The magnetic guide element 40 illustrated in FIG. 5 rests by means of aflange-shaped portion 41 on the bottom 31 of the second piston 4.Provided in the flange-shaped portion 41 is a recess 42, whichcorresponds to the second fixing element 39 and by means of which themagnetic guide element 40 is fixed and positioned on the second piston4.

The magnetic guide element 40 additionally has a peg-shaped portion 43which points in the opposite direction to the peg 25 of the first piston3 and which serves as a means for guiding a permanent magnet 44.

The magnet 44 serves as a signal transmitter for a position transmitterand generates a magnetic field radially in the direction of a sensorelement (not shown)—preferably in the form of a Hall-effect sensor, amagnetoresistive sensor or a reed contact—which is provided at a fixedlocation on the housing 2 and can be connected to an electronic controlunit (not shown) in order to permit position detection.

The magnet 44 is ring-shaped and, as is apparent, is arranged betweendisks 45, 46 of magnetic material on a cylindrical support 47 made ofnonmagnetic material, which has a collar 48 for axial support of themagnet 44.

As is apparent from FIG. 5, the support 47 with the magnet 44 is actedupon, on the one hand, by the return spring 23 of the first piston 3and, on the other hand, by another spring means 49, which is supportedon the second piston 4, with the result that the magnet 44 is as it wereclamped between the pistons 3, 4 and movable relative to the latter.However, the spring force of the return spring 23 is greater than thespring force of the other spring means 49. This allows anactuation-induced displacement of the magnet 44, even if the secondpiston 4 is fixed immovably due to a regulating operation affecting thevehicle dynamics.

In addition to the improvement in dynamics, the embodiment described ofthe second piston 4 in the two illustrative embodiments offers theadditional advantages that, for example, the overall length of themaster cylinder 1 can be shortened by means of a shorter return spring24, and the master cylinder 1 has fewer individual components overall.It is furthermore also possible, within the scope of the invention, todesign the first piston 3 with the control passages 20 described in theform of axial grooves and with the first fixing element 32.

FIGS. 6 and 7 show a piston 50 of a third illustrative embodiment, whichcan be provided as a first and/or as a second piston of the mastercylinder 1. As is apparent especially from FIG. 7, which shows anenlarged detail of the piston 50, control passages 51 of the piston 50have a control edge 52 formed parallel to a piston end face 53. Incontrast to the first two illustrative embodiments, the control passages51 are provided as radial apertures in the piston 50, which can beproduced from plastic or by means of an extrusion process, as describedabove. Here too, the parallel control edge 52 has the advantage that theflow cross section of the control passages 52 can be enlarged whilekeeping the closing travel the same, thus improving the dynamic behaviorof the master cylinder 1 during control interventions. The remainingshape of the control passages 51 can be adapted to the correspondingcharacteristics of the piston.

Another illustrative embodiment, which is not shown, envisages that thecontrol passages begin radially and continue as a groove which extendsaxially under the sealing element.

LIST OF REFERENCE SIGNS

-   1 master cylinder-   2 housing-   3 piston-   4 piston-   5 annular groove-   6 annular groove-   7 sealing element-   8 sealing element-   9 inner sealing lip-   10 inner sealing lip-   11 outer sealing lip-   12 outer sealing lip-   13 outer side-   14 outer side-   15 pressure chamber-   16 pressure chamber-   17 replenishment chamber-   18 replenishment chamber-   19 control passage-   20 control passage-   21 wall-   22 wall-   23 return spring-   24 return spring-   25 peg-   26 end-   27 stop-   28 sleeve-   29 collar-   30 collar-   31 bottom-   32 fixing element-   33 control edge-   34 control edge-   35 inner groove-   36 piston end face-   37 collar heel-   38 arm-   39 fixing element-   40 magnetic guide element-   41 flange-shaped portion-   42 recess-   43 peg-shaped portion-   44 magnet-   45 disk-   46 disk-   47 support-   48 collar-   49 spring means-   50 piston-   51 control passage-   52 control edge-   53 piston end face-   54 groove end-   A actuating direction

1.-8. (canceled)
 9. A master cylinder for a regulated braking systemhaving at least one piston, which is movable in a housing and which issealed off by a sealing element arranged in an annular groove of thehousing from a pressure chamber, which can be connected to anunpressurized replenishment chamber by control passages formed in thepiston, wherein the control passages of at least one of the pistons havea control edge formed parallel to a piston end face.
 10. The mastercylinder as claimed in claim 9, wherein the control passages areprovided as axial grooves on an outer side of the piston.
 11. The mastercylinder as claimed in claim 10, wherein the axial grooves are providedin a dovetail shape.
 12. The master cylinder as claimed in claim 9,wherein the control passages are provided as radial apertures in thepiston.
 13. The master cylinder as claimed in claim 9, wherein thecontrol passages are provided in the piston by stamping.
 14. The mastercylinder as claimed in claim 9, wherein the piston is made of plastic.15. The master cylinder as claimed in claim 9, wherein the piston isproduced by an extrusion process.
 16. The master cylinder as claimed inclaim 9, wherein the piston is of cup-shaped design with a bottom, and afirst, centrally arranged fixing element for a return spring of thepiston is provided on an inner side of the bottom.
 17. The mastercylinder as claimed in claim 9, wherein a second, centrally arrangedfixing element for a magnetic guide element is provided on an outer sideof the bottom.